Cap??tulo de livro
Is spent nuclear fuel immune from delayed hydride cracking during dry storage? An IAEA coordinated research project
Zirconium in the Nuclear Industry: 18th International Symposium
Registro en:
10.1520/STP159720160048
0000-0003-4822-8840
Autor
COLEMAN, CHRISTOPHER E.
MARKELOV, VLADIMIR A.
ROTH, MARIA
MAKAREVICIUS, VIDAS
HE, ZHANG
CHAKRAVARTTY, JAYANTA K.
ALVAREZ-HOLSTON, ANNA-MARIA
ALI, LIAQAT
RAMANATHAN, LALGUDI
INOZEMTSEV, VICTOR
Resumen
Delayed hydride cracking (DHC) has been responsible for cracking in zirconium
alloy pressure tubes and fuel cladding and is a concern for spent fuel storage.
For cracking to start, sufficient hydrogen must be present for hydride to form
at a flaw tip and the local tensile stress must be sufficiently large to crack the hydride (a crack will not extend if the threshold in the stress intensity factor,
KIH, is not exceeded. A high-temperature limit exists when the yield stress of
the cladding alloy becomes too low to crack the hydride. In this paper
we describe measurements of KIH and the crack growth rate, V, in unirradiated
Zircaloy-4 fuel cladding containing approximately 130 ppm hydrogen in the
cold-worked stress???relieved condition representing pressurized water reactors
(PWRs) and pressurized heavy-water (PHWR) reactors. Four methods are used
to evaluate KIH. The test specimen and fixture used in these methods was the
pin-loading tension configuration. The test temperature ranged from 227 to
315 C. The mean value of KIH below 280 C had little temperature dependence;
it was about 5.5 MPaHm in the PWR cladding and slightly higher at 7 MPaHm
in the PHWR material. At higher test temperatures, KIH increased dramatically
to more than 12 MPaHm, whereas the crack growth rate declined toward zero.
This behavior suggests that unirradiated Zircaloy-4 fuel cladding is immune
from DHC above about 320 C; this temperature may be increased to 360 C by
irradiation. The implications for spent fuel storage are that during early storage
when the temperatures are high, any flaw will not extend by DHC, whereas at
low temperatures, after many years of storage, flaws would have to be very
large, approaching through wall, before being extended by DHC. To date, spent
nuclear fuel is not known to have failed by DHC during storage, confirming the
inference.